Stump grinding machines are used widely for removing tree stumps using a grinding wheel, a cutting chain or other cutting instrument. The grinding wheel, for instance, is swept back and forth across a tree stump. With each sweep, the grinding wheel is lowered incrementally until the stump is removed. The final sweeps of the grinding wheel may be below ground level to ensure that the entire stump has been eliminated.
Power to drive the grinding wheel is derived from an engine, usually a gasoline or diesel engine, installed on the grinding machine. The conventional grinding machine uses a power train that directly connects the engine to the grinding wheel to transfer the engine power to the grinding wheel. If the grinding wheel becomes jammed below ground level, for instance, while removing the tree stump, an overtorque situation can occur. Such a situation can transfer shear and overload forces to the engine, particularly its crankshaft, which can result in an engine failure that is costly to repair or may require replacement of the engine.